Asphalt structural unit



United States Patent Ofifice 3,063,856 Patented Nov, 13, 1962 3,063,856 ASPHALT STRUCTURAL UNIT Harley F. Hardman, Lyndhurst, and Harvey E. Alford,

Amherst, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Nov. 5, 1959, Ser. No. 851,016 2 Claims. (Cl. 106-281) This invention relates to a light-weight asphaltic structural unit highly filled with a mass of small, hollow, holefree, glass spherical particles, and more particularly to an asphalt block for application as a roofing material which contains over 80% by volume of said small, hollow glass spheres. In the asphaltic structural unit of this invention the asphalt is present as a binder in a continuous phase, thereby distinguished from asphaltic impregnated building boards or structural units of fibre or the like in which asphalt is permitted to merely penetrate only a short distance into the side of the structural unit, leaving a core of untreated material.

Asphalt blocks, comprising essentially an oil asphalt or natural asphalt as a binder and sand as a filler, are well known to the prior art. Such blocks have been used to a limited extent as a roofing material. For this application the blocks are usually pre-cast, laid in place on a roof frame, and cemented together with a suitable agent such as asphalt, or merely laid in place on a roof frame and the whole roof then covered with a suitable layer of asphalt. These blocks, however, have the disadvantage of being quite heavy due to the high specific gravity of sand; and, consequently, when they are used for roofing, expensive framing is required to accommodate them. Furthermore, due to the weight of such blocks, serious limitations are imposed on the unit size of the blocks due to handling considerations in transportation and installation. Because of this, lighter weight materials such as expanded perlite, other expanded volcanic glass and the like have been suggested as a substitute for sand in asphalt blocks, particularly when used in roofing construction. 1

It has been found, however, that light-weight materials such as perlite and the like cannot be incorporated in the high percentages desired because the resulting composition becomes either too dry to form into a desired structural unit, or if formable the unit exhibits poor strength characteristics. Consequently, in the past the inherent benefits of the light-weight materials used could only be partially realized and the degree of improvement over sand-filled asphaltic blocks has been too limited.

One object of the present invention, therefore, is to provide an asphaltic structural unit containing a higher percentage of light-weight filler while retaining suitable forming and strength characteristics so that the optimum reduction in weight is gained and the best advantage of the other inherent virtues of the light-weight material, such as improved heat and sound insulation, is appreciated. Another object of the present invention is to offer an asphalt block which has strength characteristics as a construction material which is not only comparable to asphalt block utilizing sand as a filler, but superior thereto, particularly in resistance to deformation. A still further object of the present invention is to increase the content of an inert non-combustible light-weight filler in an asphaltic block, thereby lowering the amount of asphalt present so that the fire resistance of the unit is substantially improved.

These objects are accomplished by preparing an asphalt structural unit containing from about 80 to 96% by volume a filler consisting essentially of a mass of small, hollow, glass spherical particles. Obviously, lower concentrations of the hollow glass spheres may be used but the maximum potential lightweight and other inherent properties contributed by this unique material cannot then be gained. It will, of course, be obvious from the high percentage in which these hollow glass spheres may be incorporated that they have an unusually high affinity for asphalt whereby a uniformly thin coating of asphalt is adsorbed on the particles, making it possible for the mass of spherical particles to be bound together with only a minimum amount of asphalt.

The small, hollow glass particles in the form contemplated for the present invention are prepared from discrete particles of feed which form a glass upon fusion thereof and a blowing agent in the manner described in co-pending application Serial No. 691,726, new U.S. Patent No. 2,978,340, issued Apr. 4, 1961. The particles may be formed from any glass-forming components. A preferable feed material is disclosed as comprising a uniform mixture of sodium silicate as a primary component containing 2.5 to 25% boric acid and 0.8 to 5.0%, urea by.

weight based on the silicate as anhydrous silicate. A typical product, for example, has particles within the size range of 10 to 350 microns, with an average diameter of microns. The gas density of these particles depends primarily upon the relationship of the volume of the spheres to wall thickness. Generally, may be controlled within the range of 0.25 to 0.45 gram/ cubic centimeter (cc.), but may range from 0.1 to 0.75 gram/cc. Wall thickness of these particles is surprisingly thin and may be expressed as a percentage of the diameter of the spheres, preferably being about 0.75 to 1.5% in particles having a size of 1 to 500 microns. For. example, a sphere having a diameter of 350 microns and.

. rial No. 691,725, assigned to our assignee. The description in both of these co-pending applications is incorporated herein by reference to the extent as may be required for the clear and complete understanding of these hollow glass particles.

The asphalt ingredient of the invention may be any natural or manufactured bituminous material which may serve as an asphalt cement and may be used as such or applied in the form of a cutback asphalt or asphalt emulsion. The latter two forms, upon the evaporation of the solvent and water, respectively, leave an asphaltic residue which is similar to asphalt cement. Agents commonly incorporated in minor amounts in asphalt to increase the strength of bond or improve weatherability or other specific properties may also be added to the asphalt for the present invention if desired.

In executing the invention, the mass of hollow glass spheres is intimately mixed by any suitable means with asphalt in a molten state. For example, a ribbon mixer may be used to accomplish the mixing. The glass spheres may be treated, if desired, to facilitate the mixing. After mixing, the mixture is formed by use of appropriate molds and slight pressures into the desired shapes, which may be blocks, sheets, or any other forms required for the particular end use. The molding pressure is not critical and generally will be in the range of from 5 to 300 p.s.i. If greater strength is desired, a reinforcing agent may be added to the composition such as metal reinforcing rods, fibrous asbestos, glass fiber cloth, or nylon cloth.

The following example illustrates the best mode now contemplated for carrying out the invention.

the, density,

269 cc. of hollow glass particles preheated to 300 F. was mixed in with ll cc. of an asphalt cement having a penetration of 70/80 at 77 F., maintained at 300 F. in a one-gallon cylindrical, open-end container. The mixing was carried out by hand with use of a spatula over a period of approximately five minutes. The hollow glass particles were formed from a boro sodium silicate composition containing urea as a blowing agent and had a bulk density of 0.30 gram/00., with a size range of from 10 to 300 microns.

The resulting mixture was compressed under 50 psi. in a molding cavity having the dimensions of 6" x 6" x /2 high. The compressed mixture was permitted to cool and was self-retaining in shape thereafter. The resulting asphaltic block had a density of 0.30 gram/cc. and contained 96% by volume hollow glass spheres.

Three additional blocks were prepared in accordance with the foregoing procedure while varying the proportions of hollow glass particles to asphalt. These products, B, C, and D, and Product A, the block prepared in the working example, are compared in Table I below with parallel asphalt-sand compositions, Products A, B, C, and D prepared in a similar manner, to show the effect of composition on density.

Table I Filler Asphalt, Density, Product Hollow Sand, v01. percent lbs/i12 glass vol. percent spheres, vol. percent Compressive and fiexural strength determinations were run on specimens taken from each of the products shown in Table I. A comparison of the data thus collected showed that in addition to providing attractively light materials of construction the blocks filled with glass spheres, Products A through D, also had superior strength over corresponding asphalt-sand compositions. Further more,'the products filled with glass spheres showed considerably greater resistance to deformation than the cor-. responding products filled with sand. As illustrative of these determinations, the data obtained for compressive strength is provided in Table II below. For these tests, specimens were cut from each of the blocks measuring approximately /2" square x 1 /2 high. The compressive strength test was conducted on a Tinius-Olsen Universal Testing Machine. The compressive strain at failure values are calculated from the compressive test data and may be defined as the amount of deformation of the sample at failure divided by the original height of the sample. These values, therefore, give an indication of the dimensional stability and the lower the percentage strain value, the better is the indication of dimensional stability. The modulus of elasticity in compression is calculated from the compression test data. These values provide a measure of the amount of deformation under compressive stress which is undergone before a point of failure in the specimen is reached.

Table II Compres- Percent Modulus of sive compreselasticity Product strength sive in compresp.s.i. strain at sion, p.s.i.

7 failure It will be apparent from Table II that compositions containing the hollow glass particles not only have greater compressive strength but also do not deform nearly as much under compression. From additional testing it has been found that this superior resistance to deformation for the products containing hollow glass spheres is also observed when the stress is either tensile or flexural instead of compressive. This property of dimensional stability for an asphaltic structural unit containing hollowglass spheres provides a significant advantage when used for a roofing material because it permits the roofing material to actually contribute part of the load-bearing function, thereby providing economies in construction design. Furthermore, more satisfactory service performance can be expected for a roof prepared with this material with respect to resistance to snow loads, wind stresses, and occasional human activities on roof areas for repair or other maintenance functions.

Although an asphaltic structural unit highly filled with hollow glass spheres is considered particularly desirable for application as a roofing material due to its light weight and exceptional strength characteristics, it will be clear that such a structural unit obviously may be used broadly as a material of construction and the invention is certainly not to be limited to roofing applications. The contemplated structural unit may be in the form of a block, sheet, or other convenient form and as such may be used, for example, to form walls, floors or roadways, or serve as an insulation liner for refrigerators, freezers, and the like.

We claim:

1. An asphaltic structural unit consisting essentially of from about 4 to 20% by volume of an asphalt cement and from about to 96% by volume of hollow glass spherical particles having an average diameter of from about 1 to 500 microns and a gas density of from 0.1 to 0.75 gram/cc.

2. An asphaltic block for use as a roofing material consisting essentially of from about 4 to 20% by volume of an asphalt cement and from about 80 to 96% by volume of hollow glass spherical particles having an average diameter of from about 1 to 500 microns and a gas density of from 0.1 to 0.75 gram/cc.

References Cited in the file of this patent UNITED STATES PATENTS 225,991 Lee Mar. 30, 1880 2,625,512. Powell Ian. 13, 1953 2,797,201 Veatch June 25, 1957 2,861,895 Hardman Nov. 25, 1958 2,892,592 Greene -1 June 30, 1959 

1. AN ASPHALTIC STRUCTURAL UNIT CONSISTING ESSENTIALLY OF FROM ABOUT 4 TO 20% BY VOLUME OF AN ASPHALT CEMENT AND FROM ABOUT 80 TO 96% BY VOLUME OF HOLLOW GLASS SPHERICAL PARTICLES HAVING AN AVERAGE DIAMETER OF FROM ABOUT 1 TO 500 MICRONS AND A GAS DENSITY OF FROM 0.1 TO 0.75 GRAM/CC. 